Couch-potato lifestyles making the nation tip the scales into obesity

A LACK of exercise, rather than diet, is the main cause of the obesity epidemic, new research reveals.

Sedentary lifestyles and lack of exercise are blamed for the rise in obesity rates [GETTY]

A study in the US found over the past 20 years activity levels have fallen dramatically as average body mass index (BMI) has risen.

But the amount of calories consumed has remained the same.

Scientists say a nationwide drop in leisure time exercise, especially among young women, may be responsible for the upward trend in obesity rates.

It is recommended adults do 150 minutes of moderate exercise, such as brisk walking, cycling or gardening, each week. Studies have shown about two in three adults in the UK fail to achieve this.

Fewer manual jobs, more cars and home entertainment technology mean most people get much less exercise now than their parents or grandparents did.

Two thirds of men and almost six in ten women in the UK are overweight or obese. In Western Europe, just Iceland and Malta have more.

By analysing data from the National Health and Nutrition Examination Survey (NHANES) researchers found the number of US women who reported no physical activity jumped from 19.1 per cent in 1994 to 51.7 per cent in 2010. For men, the number rose from 11.4 per cent to 43.5 per cent.

During the period, average BMI has increased across the board, with the most dramatic rise found among young women between 18 and 39.

Professor Uri Ladabaum, of Stanford University, California, said: "These changes have occurred in the context of substantial increases in the proportion of adults reporting no leisure time physical activity, but in the absence of any significant population level changes in average daily caloric intake.

"At the population level, we found a significant association between the level of leisure time physical activity, but not daily caloric intake, and the increases in both BMI and waist circumference."

Adults are recommended to do a minimum of 150 minutes of exercise a week [POSED BY MODEL/GETTY]

We found a significant association between the level of leisure time physical activity, but not daily caloric intake, and the increases in both BMI and waist circumference

Professor Uri Ladabaum

The study published in the American Journal of Medicine looked at the escalation of obesity in terms of both exercise and caloric intake.

While the researchers did not examine what types of foods were consumed, they did observe total daily calorie, fat, carbohydrate, and protein consumption have not changed significantly over the period, yet the obesity rate among Americans is continuing to rise.

Researchers also tracked the rise in abdominal obesity, which is an independent indicator of mortality even among people with normal BMIs.

This is defined by a waist circumference of at least 34.65 in (88cm) for women and 40.16 in (102cm) for men.

The average increased by 0.37 per cent and 0.27 per cent respectively, per year. Just like the rise in average BMIs, the group most affected by increased rates of abdominal obesity was women.

Prof Ladabaum said: "The prevalence of abdominal obesity has increased among normal weight women and overweight women and men.

"It remains controversial whether overweight alone increases mortality risk, but the trends in abdominal obesity among the overweight are concerning in light of the risks associated with increased waist circumference independent of BMI."

While increased calorie intake is often blamed for rising rates of obesity, no association between these was found in this study. In contrast, an association was found between the trends over time for lack of physical activity and high BMI numbers.

Added Prof Ladabaum: "Our findings do not support the popular notion the increase of obesity in the United States can be attributed primarily to sustained increase over time in the average daily caloric intake of Americans."

Identifying the link between the drop in physical activity and increased BMIs, as well as the groups particularly affected, can assist public health officials to develop targeted, effective interventions against the obesity epidemic.

Journal editor Pamela Powers Hannley said: "If we as a country truly want to take control of our health and our health care costs, the Ladabaum et al paper should be our clarion call.

"From encouraging communities to provide safe places for physical activity to ensuring ample supply of healthy food to empowering Americans to take control of their health, we must launch a concerted comprehensive effort to control obesity."